With advances in high speed data transmission techniques, systems for transmitting data via telecommunication links have become ubiquitous in the modern office environment. Data transmission systems such as facsimile machines or modems provide the ability to transmit data or documents around the world within minutes rather than the hours or days required to deliver them via conventional methods such as by courier or through the mail.
Most data transmission systems operate under the control of a computer processor without human supervision. For example, most facsimile machines can scan and store a plurality of documents in their internal memory and transmit them sequentially to a predetermined or specially entered telephone number. While this process generally works well, currently existing facsimile machines cannot recover from an error in the telephone number of the called party or receiving facsimile machine.
Currently, the most common method of informing a user that a problem has occurred with the number dialed is to use an informational error message that is played by the telephone service provider. Such messages are usually preceded with a series of "alert tones" that have a predefined frequency or pitch. For example, when the telephone number of a desired party or receiving facsimile machine has been changed, the informational message is usually something like: "The number you have reached has been changed. The new number is 555-1234. Please make a note." Despite the fact that an informational message is played by the telephone service provider, currently available computerized data transmission systems cannot interpret the message and will continue to dial the original number again and again before terminating with an indication that a connection was not possible. If a human operator is not available to correct the problem, there is a chance that the data to be transmitted will never reach the intended recipient.
Given the shortcomings in prior art computer-based data transmission systems, there is a need for a data transmission system that can detect and respond to an error in a telephone call in order to increase the speed and accuracy with which data are transmitted.